As potential therapeutic agents, in the treatment of inflammatory and other conditions, there is considerable interest in compounds that have the ability to inhibit matrix metalloproteinases and also the release of tumour necrosis factor. Two known compounds of this type are 2S-[4-(2, 5-dioxopyrrolidin-1-yl)-2S-mercaptobutyrylamino]-4-methylpentanoic acid (2,2-dimethyl-1S-methylcarbamoylpropyl)amide (herein Compound A) and 2S-[2S-mercapto-4-(3,4,4-trimethyl-2, 5-dioxoimidazolidin-1-yl)butyrylamino]-4-methylpentanoic acid (2,2-dimethyl-1S-methylcarbamoylpropyl)amide (herein Compound B). Compound A is disclosed in WO-A-96/11209 and WO-A-98/39024. Compound B is disclosed in WO-A-97/12902 (generically) and WO-A-98/39024 (specifically).